The promised rebellion, according to the very excellent Philip Cowley of Nottingham University – the Bill Frindall of parliamentary rebellions – would not only be Mr Cameron’s biggest revolt – if it tops that magic 41 – but it would also be the largest revolt ever by Conservative MPs in government over Europe. Period, as the Americans say.

The issue at hand in the House of Commons vote at 10pm may be a piece of so-called backbench business on a motion that is binding on no-one, but it matters.

It matters not because it would force anyone to hold a referendum on Britain’s membership of the European Union. It would not. But it matters because of what it tells us of Mr Cameron’s fractious relationship with his MPs and the potential consequences for the management of the coalition government.

The rest of that, which is quite an extended think-piece, is well worth the visit.

Now let’s do the math, also “as the Americans say”.

There are 306 Tory MPs.

Note: we now need to focus on the Tory contingent of the ConDem politburo. Sixteen of them are full Cabinet rank. Five more attend Cabinet, with a sixth (Attorney General Dominic Grieve) when he is summoned. Twenty-one are Ministers of State and such-like.

That gives a core “pay-roll vote” of 16+5+1+21= 43.

Plus another score or so “Parliamentary Private Secretaries” and bag-carriers (Malcolm can definitely count fifteen from last June, and others seem to have accreted subsequently). Which is taking us up to the low 60s.

Then there are those who have been discreetly promised preferment at some later stage. Or those whose self-regard assumes that their lust for a post will be satisfied if they keep noses clean long enough (believe it or not, Nadine Dorries was having herself touted in those terms — see Iain Dale passim — before the Election).

Should the worst (from Cameron’s and the Whips’ point of view) scenario come to pass, and the rebels amount to around 80, going a third of the backbench Tories will have shown their scorn for this Prime Minister and his cock-up of party management.

That more than a third of his backbenchers are planning to rebel against him less than 18 months into government is not a good sign. It should make him overhaul his whole approach to party management, to spend far more time wooing his own side. As one Minister says: ‘He’s got to run two coalitions: one with the Lib Dems and one with his own party.’

68 (or thereabouts): The number of Tory MPs who have already signed up to Nuttall’s motion. They include the chairman of the 1922 Committee, Graham Brady, and Stewart Jackson, PPS to Owen Patterson.

41: The size of, as Cowley and Stuart put it, “the largest Conservative Government backbench rebellion on Europe on whipped business” — suffered by John Major on 20 May 1993. 41 is also the size of the largest Tory rebellion so far this Parliament.

75: The size of the coalition’s effective majority in Parliament, which would be an embarrassing milestone were it to be exceeded. Cowley and Stuart advise caution about predicting rebellions, but they do add that, “if you combined the list of those Conservative MPs who had signed the referendum with those who have already defied their whips over Europe since May 2010, you got a figure of 78.”

139: The biggest rebellion against any party whip since the 19th Century. And the party whip in question? Labour’s, during the March 2003 vote on the Iraq War.